Compared to warping space to fly faster than light, the energy use is insignificant, otherwise Quark and Rom would have been sterilized when they were carrying around a turned on cloaking generator in the Emperors new Cloak, that was not connected at all to any external power sourses.
Similar arguments could be made for Enterprise in the Romulan Incident, about Enterprise not needing a larger warp reactor to power the first cloak when it was first plugged in, after Kirk stole it.
Although I think that power use has been cited for why it's impossible to cloak while your shields are up, which hasn't been true since Star Trek 6. With more modern cloaks, I think there's just a conflict, trying to suppress the signature of a massive energy field radiating off the ship that can more easily be turned off, than figured out how to invisiblize.
Speed.
Cloaks destabilized and work less well at higher warp speeds, and maybe higher impulse speeds, since full impulse through real space probably puts more stress on the ship than high warp inside a warp bubble.
Oh? Decloaking to fire? Yeah, but is that about power consumption issue, or are you just a ninny if you forget to turn your shields on for a couple seconds while you're firing disrupters?
OH!
Passive scans only. You may be invisible, but you're also flying blind almost. No active scans, and no long range scans, so an entire flotilla can easily sneak up on you if you are too cloaked, when you should be mindful of your surroundings.
